Network Synchronization among Femtocells

To successfully deploy femtocells overlaying the Macrocell as a two-tier that had been shown greatly benefiting communications quality in various manners, it requires to mitigate cross-tier interference between the Macrocell and femtocells, as well as intra-tier interference among femtocells. For this purpose, solutions for interference mitigation have been proposed for femtocells in literatures. However, an essential assumption of these solutions is that all femtocells and the Macrocell shall be synchronized. Such a (network) synchronization of the Macrocells and user deployed femtocells create diverse challenges from conventional synchronization among Macrocells. Existing solutions therefore leverage the global positioning system (GPS) or the wired backhaul (IEEE 1588) to synchronize the Macrocell and all femtocells, however, they are infeasible for LTE-Advanced femtocells suffering a severe penetration loss of GPS signals and a severe jitter on the backhaul with heterogeneous protocols. As a consequence, each femtocell achieving a timing consensus by leveraging synchronization signals broadcasted by the Macrocell or by the neighboring femtocells turns out to be the possible solution. In this paper, we propose a network synchronization algorithm for femtocells. By only utilizing existing synchronization signals, the proposed network synchronization algorithm achieves the timing consensus among femtocells with and without the present of the Macrocell. Yielding an extremely low computational complexity, the proposed algorithm achieves the essential assumption of interference mitigation solutions in literatures and thus enabling the femtocell technology.